Tuesday, August 9, 2011

GASTROINTESTINAL VIRAL INFECTIONS

Types:

A.Enteroviruses.

B.Rotavirus.

C.Hepatitis A virus.

D.Small round-structured viruses.

A.Enteroviruses:

Enteroviruses are a genus of Picornavirus family and include Coxsackieviruse group A (types 1-22, 24) and group B (types 1-6), Echoviruses (types 1-9, 11-27) , Polioviruses, and newer Enteroviruses (types 29-34, 68-71).Enteroviruses have diameter 24-30 nm and have icosahedral structure single strand RNA. They are transmitted by the fecal-oral route, but coxsackievirus A21 spread by droplet transmission, and other enteroviruses are probably spread by this route. Virus shedding in the oropharynx and in feces may continue for at least one month after infection .

Asymptomatic infection is common with all enteroviruses, but also associated with a wide spectrum of clinical syndromes. These range from nonspecific febrile illness and rashes to the divesting paralysis of spinal or bulbar poliomyelitis, meningitis and encephalitis. Nosocomial outbreaks of non-polio enteroviruses have been particularly severe in neonatal units and nurseries .

Isolation of infected individuals is critical in the control of non-polio enterovirus infection. Applying rigorous hand washing and virological surveillance to monitor any cross-infection. Poliovirus is unlikely to pose a problem of nosocomial infection in the industrialized world, and with imminent global eradication of polio, the problem should cease to exist in all countries. In the meantime, the higher risk of vaccine induced paralytic poliomyelitis in adults than in children means that unvaccinated parents of children who have received oral polio vaccine and any unvaccinated ward staff should be immunized .

Immunocompromised contacts should be offered inactivated polio vaccine. In U.S., continued occurrence of vaccine-associated paralytic poliomyelitis has led to recommendations for a progressive change to the use of inactivated polio vaccine for childhood immunization.

B.Rotavirus:

Rotaviruses are classified as a genus in the family Reoviridae. The term rotavirus is derived from the Latin word Rota, which means wheel. Rotaviruses have a distinctive morphologic appearance by EM. Complete particles measure about 60-80 nm in diameter and have a distinctive double-layered icosahedral capsid, double-stranded RNA . Rotavirus infection causes sudden onset of fever, abdominal pain, and vomiting, followed by watery diarrhea that lasts for 4-7 days. The incubation period is short (1-2 days). The clinical presentation is varied, but vomiting and dehydration are prominent features.

Rotaviruses are recognized as an important cause of nosocomial infection, particularly in infants and children under the age of 5 years and in the elderly. They may also cause gastroenteritis in the immunocompromised. Rotaviruses have been found to cause 45% of pediatric nosocomial gastroenteritis. Studies demonstrated transfer of infection within single rooms or wards but not from one room or ward to another. Thus in these particular outbreaks, there was no evidence that staff were acting as vectors of infection within the hospitals .

C.Hepatitis A virus (HAV):

On the basis of several features that distinguish HAV from other Picornoviruses, it is classified as the only member of the Hepatovirus genus of the Picornoviridae family. The HAV virion appears as a relatively smooth, 27-30 nm rounded particle. Icosahedral capsid, single strand RNA. Nosocomial transmission of HAV has been associated with poor hygienic practices and crowded conditions. Transmission from patients to staff has occurred, usually as a result of contact with asymptomatically infected children or adults with vomiting, diarrhea, and fecal incontinence.

An outbreakwas reported in a burn unit in which a father and son, both with severe burns, transmitted HAV to 11 health care workers and another patient, all of whom developed clinical hepatitis. As in other episodes of nosocomial transmission, in this outbreak infection control in the unit was suboptimal, and food had been shared. Food-borne outbreaks of HAV in hospitals have usually involved staff and often also small numbers of patients. As with other types of hepatitis, the clinical effects of HAV infection range from asymptomatic attacks to nonspecific febrile illness to classical acute hepatitis with jaundice.

Maximum fecal shedding of HAV occurs in the late incubation period. Care should be taken in handling excreta, and single room isolation should be used if the patient is incontinent of feces. Human normal immunoglobulin may be administered prophylactically in the events of significant exposure to HAV positive material. There is evidence to support the use of HAV vaccine for prophylaxis following exposure to the infection. Hepatitis A vaccination may be considered for personnel working in health care setting where HAV infection is endemic.

D.Small round-structured viruses(SRSVs):

Norwalk virus – like agents causing gastroenteritis outbreaks as Caliciviruses (30-40nm in diameter) or Astroviruses (28-30 nm); collectively are known as SRSVs. Outbreaks of gastroenteritis due to SRSVs occur in schools, families and hospitals and can involve any age. Vomiting is a prominent feature, and high virus titers in vomitus are responsible for widespread transmission in closed areas.